The Synthesis and Characterization of Functionalized Nanothreads
Open Access
- Author:
- Koeplinger, Daniel Brian
- Graduate Program:
- Chemistry
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 08, 2019
- Committee Members:
- John V Badding, Thesis Advisor/Co-Advisor
John B Asbury, Committee Member
Benjamin James Lear, Committee Member - Keywords:
- Nanothread
Benzene
Compression
Polymerization
Diamond Anvil Cell
Exfoliation
AFM - Abstract:
- Carbon nanothreads are a relatively new type of carbon material which has an sp3 structure similar to diamond, but extends in only one dimension. The predicted properties of nanothreads are extraordinary, rivaling other recent carbon materials such as carbon nanotubes and graphene in both strength and stiffness. Nanothreads are synthesized experimentally by slow compression of benzene to about 20 GPa, followed by slow decompression, resulting in a crystalline product in which the polymer is arranged into a hexagonally close-packed structure. The material can be identified via its characteristic six-fold diffraction pattern, as well as its Raman and IR spectra. In addition to nanothreads produced from benzene, several new types of nanothreads have also been synthesized from other precursors, such as pyridine and aniline. In Chapter 2.1 of this work, experiments involving the compression-induced polymerization of three additional aromatic molecules are described. Toluene produced the most promising results, yielding a transparent amorphous solid which has similar IR and Raman spectra to those of previous nanothreads. Nanothread syntheses were also attempted using benzoic acid and hexabromobenzene as precursors, but no significant reaction was seen for either material. Nanothread structure is complex, and there are many structures of similar energy which are thermodynamically possible. In addition to the fully-saturated sp3 products from a Degree-6 polymerization, products which result from incomplete polymerization, including unsaturated Degree-4 and Degree-2 segments, are observed. Each of these structures has varying amounts of sp2 character. A series of experiments are described in Chapter 2.2 in which the ratio of sp2 to sp3 bonds in the nanothread product was measured via advanced solid-state NMR. These ratios were used to approximate the relative quantities of Degree-2, -4, and -6 structures for both benzene and pyridine nanothreads. NMR data was also used to constrain which isomers of each Degree might be found in experimentally-synthesized nanothreads. When nanothreads are formed under pressure, they produce crystals of close-packed fibers. These fibers are bound together primarily by Van-der-Waals forces, and application of mechanical force could theoretically exfoliate individual threads from the bulk. In Chapter 3, exfoliation experiments are described in which three separate methods attempted to separate individual threads from the bulk: applying shearing forces by twisting samples between two planes, peeling fibers away from the bulk using tape adhesive, and crushing the nanothread crystals with the tip of a diamond. Samples from each of these methods were examined by atomic force microscopy. Identification of individual fibers separated from the bulk nanothread crystal proved problematic because of the small radii of nanothreads, particularly when compared to the resolution of techniques used to characterize nanothreads in the bulk. As a result of these limitations, the only way to prove that a fiber was a nanothread would be to find a thread still partially attached to the bulk. No partially-attached fibers were observed by AFM using the three preparation methods listed above, but the possibility of identifying such a feature in the future was not excluded.